line of the process and has its external opening in a pore just at the joint where the chilidium meets the apex of the valve.

Teeth. In the pedicle valve, in front of the area, and separated from it by grooves, are two strong crenulated teeth which fit into sockets on either side of the platform of the cardinal process. These teeth seem to have practically the same form and position in all stages, but as they fit at such an angle in their sockets that it is almost impossible to separate the valves without breaking them, it is only rarely that a young specimen retains them. They have been seen in no

specimens less than two mm. in length.

Septum. In front of the bases of the crura there arises a rather thick, low, septum, which, about midway of the shell, increases abruptly in height till it reaches nearly to the opposite valve, then falls off less rapidly and terminates at a point which is about one fourth the length of the shell from the anterior margin. From the point where it begins to rise it is thin and sharp. This septum is well developed in young stages. A specimen 2 mm. in length has a septum exactly similar to that of the adult.

material.

Brachidium. — Only a part of the loop has been seen in the present One adult specimen has two quite stout lamelle which extend upward and slightly inward and reach about half way to the highest point of the septum. At their anterior ends they are flattened and turned slightly outward. Near the posterior ends are what appear to be the bases of processes which would have extended outward and upward. Another specimen, 2 mm. in length, shows about the same amount of the loop, but the two lamellæ diverge at a greater angle.

Punctæ. The shells are very highly punctate, especially toward the front. From the point where the plications begin, up to a length of about three mm., the punctæ are confined principally to the depressions between the plications. There are two rows to each furrow. From that point they are scattered abundantly all over the surface.

The Same Fossil from Other Localities.

Calcified specimens from Ludlowville, Moscow, York, East Bethany and Eighteen Mile Creek, N. Y., were taken for comparison with the specimens in the present collection. Those from Ludlowville, York, and Eighteen Mile Creek resemble closely in size, index, and form, the specimens from Canandaigua Lake. Those from Moscow and

East Bethany are of larger size, have a higher index, and show a greater number of senile individuals.

The individuals from Ludlowville have, in the adult condition, the width of the hinge about equal to the width below, and most of them have the length nearly equal to the width, thus giving a low average index. The lowest index was 1.07 and the highest 1.33. The The largest specimen was 22 mm.

1.17.

average of ten adults is long and 25 mm. wide. A single specimen showed, on one margin, two plications which had bifurcated in front of the last growth line. This is an unusual condition, although Hall figures a senile individual which has all the plications of the dorsal valve bifurcated in front. (Pal. N. Y., Vol. IV, pl. 62, Fig. 3e.)

The specimes from York are small. long and 22.4 mm. in width.

The largest one is only 19 mm.

The index, average of ten specimens,

is 1.21. The range is 1.09 to 1.29.

In the collection from Eighteen Mile Creek there are specimens from 3.8 mm. by 3.2 mm. up to 20.4 X 25 mm. The index varies from .84 to 1.30, and the average of ten adults is 1.22. The mature specimens retain a neanic character in having the median plication of the ventral valve only a little stronger than the neighboring ones. Many individuals have the strong angular type of plications.

From East Bethany there are numerous specimens ranging from II X 13 mm. to 27 X 37 mm. The index varies from 1.13 to 1.44 and the average for thirty-five specimens is 1.27. Of the 510 specimens examined, nineteen per cent. showed senile characters. These individuals are mainly larger than the average adults, but the index has almost identically the same range as in the adults, viz. 1.13 to 1.44 as compared with 1.13 to 1.42. There are in the collection from this place no distinct varieties, but the long forms, 22 × 25 mm., index 1.13, grade by numerous intermediate steps into the wide forms, 19 X 27 mm. index 1.42. The number of plications varies from 17 to 28. There are only a few specimens from Moscow, but they agree in proportion and form with those from East Bethany. The average of the indices is 1.24. The largest specimen is 26 X 32

mm.

The facts would seem to indicate that, while the conditions at Canandaigua Lake were favorable for the production of large numbers of individuals of this species, they were not such as to allow them to reach the maximum development possible before the senile stage of their lives.

Trigeria lepida Hall.

Hall, Pal. N. Y., VIII, Pt. 2, 1893, pl. 50, figs. 36-40.

There are in the collection, about fifteen specimens of Trigeria lepida, three of which are adult individuals. The smallest specimen is 1.09 mm. long and .93 mm. wide: the largest is 6.8 mm. long and 6 mm. wide. The largest specimen is smaller than the smallest one figured by Hall. That is 7.8 mm. long and 6.7 mm. wide, while the largest is 11 mm. long and 9.5 mm. wide. According to that author, an adult has from 20 to 25 plications.

FIG. 31. Tri

geria lepida Hall; young individual, before the incep

Description of Smallest Specimen. — The smallest individual is roughly triangular in outline, the rostrate beak, which projects .25 mm. beyond the hinge, forming the apex. The ventral valve is convex and smooth without folds on sinus. The delthyrium is narrow and open. The dorsal valve is convex, nearly as deep as tion of plica- the ventral, and has a deep, narrow median sinus. There are no striæ. This valve is oval in outline, and wider 84 mm., width .93 mm.

tions. X16.

than long. The length is

A narrow form, only a dimensions.

width 1 mm. (Fig. 31).

little longer than this, has the following Length, ventral valve 1.36 mm., dorsal valve 1.20 mm.,

In this stage the form is very suggestive of Centronella

Changes During Development.

Outline. The outline changes very little during development, except in the amount of extention of the ventral beak. In the very small specimens, less than 2 mm. in length, the length of the ventral beak, behind the apex of the dorsal valve, is from .23 to .26 of the length of the shell. In older stages the beak is much less prominent. In a specimen 3.4 mm. long the beak is only . 19 of the length, at 5.5 mm. long it is .15 and on the largest specimen, 6.8 mm. long, it is only .09 of the length (Fig. 32).

There are, in all stages, both broad and narrow forms. In the broad form, the index is about .85 in the young specimens and .90. in the adults. For the narrow forms it varies from .73 to .80. In the adults of the broad form, the dorsal valve is about as long as wide, and is only a little longer than wide in the narrow form.

Striæ. valve.

A specimen 1.87 mm. long has seven striæ on the ventral The median one is stronger and a little longer than the others. A specimen 3.4 mm. long has 15 striæ and the largest specimen has the same number on the ventral valve and 14 on the dorsal. A smaller specimen, 3.46 mm. long, has 18 striæ on the dorsal valve and another, 5.5 mm. long has 16 striæ on one valve and 17 on the other.

FIG. 32. Trigeria lepida Hall; series showing the growth of the deltidial plates and the encroachment of the pedicle upon the ventral beak.

8.

Deltidial Plates. None of the specimens less than 3 mm. long, show any traces of deltidial plates. The specimen 3.4 mm. long shows a very narrow scalene triangle on each side of the delthyrium. In the specimen 5.5 mm. long these triangles have become wider at the base, almost uniting. The apex of the ventral beak is encroached upon, thus enlarging the opening posteriorly. In the largest specimen the deltidial plates are still wider at their lower ends and are united for a short distance. The pedicle has encroached still further upon the ventral beak, forming a large oval opening.

Sinus. The sinus in the dorsal valve is still sharp and distinct in a specimen about 3.5 mm. long, but, on the larger specimens, it is hardly perceptible.

Eunella lincklæni Hall.

Hall, Pal. N. Y., IV, 1867, p. 397, pl. 60, figs. 49–65.

Of this species there are about forty whole specimens retaining both valves and nearly as many separate valves. The smallest specimen is 1.17 mm. long and .84 mm. wide; the largest 19 mm. long and 17 mm. wide. So perfect is the preservation that in many cases a large part of the delicate loop which supported the brachia is preserved and, in at least one case, the loop is entire and as well shown as in the most perfect recent brachiopods of this type.

Description of Smallest Shell. - No stages earlier than that represented by the smallest shell in the collection could be made out. At that stage the shell is about three-fourths as wide as long, and the two

valves are subequally convex, the ventral valve a little the deeper. The dorsal valve is elongate oval, .87 mm. long and .84 mm. wide, while the ventral valve has a narrow rostrate beak which extends .2 inm. back beyond the hinge. The delthyrium is large, triangular and without deltidial plates (Fig. 33). The loop of this specimen can not be determined as only a short portion is retained. On the dorsal beak the first punctæ can be seen and their arrangement agrees with that seen on the nepionic shell of Terebratulina septentrionalis.1

FIG. 33. Eunella linckiæni Hall. Young specimen with open delthyrium. X 16. FIG. 34. The same species. An adult, showing several growth stages. X3. The first pair of punctæ are .072 mm. from the beak and in front of them, on the median line, and .109 mm. from the beak, is a third one. Beyond this they are scattered sparingly over the surface for a short distance but toward the front of the shell they become very

numerous.

Changes During Development.

Outline. -The outline changes very little during the various stages. There are both broad and narrow forms. The index of the ventral valve varies from .68 to .88 in young specimens and from .76 to .92 in adults. The dorsal valves of adults of the broad type are nearly circular, while the index of the same valves in the narrow form is from .71 to .88.

Convexity of Valves. In young stages the ventral valve is slightly deeper than the dorsal, but in the adult the convexity of the valves is often reversed. The ventral beak extends straight beyond the hinge. in young individuals. In adults the umbo is incurved and the apex of the beak is truncated by the pedicle opening.

1E. S. Morse, Memoirs Boston Soc. Nat. Hist., Vol. V. No. 8, 1902, pl. 62, fig. 15, also Mem. Bos. Soc. Nat. Hist., Vol. II, pt. 1, No. 2, pl. I, fig. 3.